A sucker rod is a rigid rod used in the oil industry to join together the surface and downhole components of a reciprocating piston pump installed in an oil well. These rods are typically between 25 and 30 feet (7 to 9 meters) in length, and threaded at both ends.
Prior art discloses a method of hardening rods such as sucker rods with the help of a device with two heads that have the ability to clamp two ends of the rod in need of treatment or modification. See Russian patent RU 2082590. In this embodiment, typically one head turns uncontrollably with the rod treated along its longitudinal central line. Unfortunately, use of the aforementioned device can result in deformation of standard length sucker rods due to tension and torsion, even though cold working the rod's surface would improve the fatigue strength and the efficiency. Additionally another shortcoming of this known method lies in the fact that this device method will not reclaim the proper geometric shape of the rod and eliminate the inner stress in it, which deteriorates the quality of the remanufactured rod and its service life.
Additional methods of remanufacturing sucker rods for re-use is to eliminate the fatigue stress in the used rods by a method involving thermally treating the rods at a temperature between about 200° C. and about 650° C. for 15 to 30 minutes. It consists of normalization, upgrading or tempering, with reference to the material or rods remanufactured. After thermal treatment the rods are straightened while still hot to achieve the required straightness. Additionally, straightening while still hot allows for the removal of stress which can occur otherwise during the course of the straightening procedure.
Typically, in such implementation, the rods undergo shot peening. Shot peening is a cold working process used to produce a compressive residual stress layer and modify mechanical properties of metals. It entails impacting the surface of a metal with shot (round metallic, glass, or ceramic particles) with force sufficient to cause plastic deformation. The shot peening process used on the reclamation of sucker rods removes scale, localizes micro-cracks and improves fatigue strength.
However, the shortcomings of this aforementioned method lie in the fact that worn out or corrosion damaged rods still retain all outside geometrical form defects, even after thermal reclamation.
It would therefore be desirable to create a more efficient method for remanufacturing standard length rods such as sucker rods that would make it possible to improve the quality of the products and decrease defects as compared with the reclamation processes delivered by traditional methods.